The present invention relates to an improved brake monitoring system, particularly for use on vehicles such as a tractor and trailer combination.
In the prior art, heavy duty trucks and other large vehicles are typically equipped with an air brake actuating system. The air brake actuating system applies air to a service chamber to move a diaphragm in a first direction. A push rod typically moves with the diaphragm, and the push rod is connected to a linkage that actuates the vehicle brakes. An emergency chamber is generally also attached adjacent to the service chamber, and is operable to move the push rod in the event that the air system fails. To this end, a high strength power spring is typically incorporated into the emergency chamber to actuate the push rod when there is a failure in the system air line. This spring also typically actuates the push rod when the vehicle is parked.
A brake actuator has a predetermined amount of available movement, or stroke, for the push rod. The amount of movement of the push rod required to fully actuate the brakes must be carefully monitored such that it is within the stroke of the brake actuator. The prior art has experienced situations wherein there has been an excessive amount of push rod movement for actuation of the brake system. This excessive required push rod movement can be created by any one of several factors. Typically, excessive movement is due to brake lining wear. As the brakes wear, more movement of the push rod is required to actuate the brakes. Further, as the linkages, connections, etc. between the members connecting the push rod to the brakes bend or become loose or excessively worn, additional push rod movement may be required to adequately stroke the brake. A combination of these several features may sometimes cause the amount of push rod movement required to actuate the brakes to approach the available push rod movement, or stroke, from the brake actuator. This is, of course, an undesirable situation.
The prior art has attempted to monitor the amount of push rod movement during actuation of the brake, and provide some indication to an operator of when there is excessive push rod movement. The determination of when there is excessive push rod movement is dependent upon the designed stroke, or rated stroke, of the brake actuator. In addition, an apparatus known as a slack adjuster is typically placed between the push rod and the foundation brake. The slack adjuster is incrementally adjusted to compensate for slack in the braking system and to decrease the required push rod movement. Automatic slack adjusters are now available which automatically adjust the foundation brake system.
Electronic indicator systems have been proposed. However, there are several obstacles to overcome. First, powering and monitoring electronic indicators on each of the brake actuators on an 18-wheel vehicle is costly. The cost in wiring alone for the vehicle exceeds the cost of all the electronic indicators and monitoring equipment combined. Further, the hostile environment in which the brake actuators are mounted can damage the wires connecting the brake actuators to a controller.
Further, there are numerous configurations for the tractors as well as the trailers. For example, the number of axles on tractors and trailers can vary. Each axle may include a spring brake actuator or just a service brake actuator. For efficiency, it would be desirable to have a single electronic controller which could be permanently programmed to recognize the specific configuration of the vehicle on which it is installed.
The present invention provides a brake monitoring system including a plurality of brake monitors mounted on each of a plurality of brake actuators on a vehicle. Each of the brake monitors includes at least one magnet and a magnet sensing device which move relatively during brake actuation, and move increasingly as the brake wears. The brake monitoring system further includes a controller receiving a signal from each of the magnet sensing devices, a brake signal indicating when the brake actuator is activated by a driver and pressure signals from each of the brake actuators indicating when air pressure in each brake actuator reaches a predetermined level. Each brake monitor further includes an RF transmitter which periodically transmits the condition of the brake actuator to the controller.
Each magnet is preferably formed on a generally hollow cylindrical sleeve which is mounted to a push rod in the brake actuator. As the push rod is actuated, the sleeve moves relative to a plurality of switches embedded in a stone shield in the brake actuator. As the brake actuator is actuated, the sleeve moves relative to the magnetic sensing device, thereby generating a signal indicative of the displacement of the push rod.
In one embodiment, the sleeve includes a plurality of magnets secured to the sleeve. In other embodiments, the sleeve comprises particles in a nylon matrix. Portions of the sleeve are selectively magnetized or the sleeve is magnetized from one axial end to the other axial end. The magnetization of the sleeve at one axial end is high and decreases linearly to the opposite axial end. A hall effect device mounted in the stone shield detects the level of the magnetic field and determines the displacement of the push rod accordingly.